DS's sleep is bonkers at the moment, no idea why!

[SleepDeprivedGrumpyBum]

DS is 17 weeks old, and for the past four nights his sleep has been truly weird and at completely opposite ends of the spectrum.

Saturday night he slept from 7pm - 12.30, then until 3.30 then up for the day at 6am. This is a good night for us, DS hasnt had that long a stretch since xmas.

Sunday night he woke at 11pm and was then up every 2 hours until 7am

Monday night was the best night i've ever had with him. 7 - 12.30, then 4 am and stayed asleep until 7 am........

but then last night he woke at 10.15pm and was up every 2 hours which is the worst night i've had with him since he was about 2 weeks old.

I've not done anything different day to day, his naps and feeding are the same; he's not teething or ill. I just dont get how it can go from the best night to the worst with very little intermission!

babies are weird!!

meant to say, i know theres sometimes a sleep regression at 4 months; but i thought that would consist of a few weeks of terrible sleep. Just find the yoyo-ing between the two types of night hard to get my head around.

Hi sleepdeprived my DD is much the same at 16wo. She has alsways been a 'bad' sleeper. Naps are now pretty consistent and mostly in her cot. She can self-settle and does sometimes.
Nights go 7pm to 10pm then feed (even if I try to wait she wakes up for this) then can go to 02.45 at the latest,(feed) then 0600 - and up. The next night she might wake twice before 10pm, then again at 00.30, then again at 2am (feed), then at 4ish and finally 6.
I have no clue as to why she wakes up loads one night then much better the next. She has a regular daily routine and naps don't seem to make a difference!
She is ebf and this month has slipped of the 50th centile?????? (she has recently started 4hrly feeds rather than 3hrly - her choice).
I have no advice (and no clue) but thought I would share. COuld it be the 4 mnth sleep regression?
Anyone?